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Flashcards · 9700 · A Level Topic 19

Genetic technology (A Level) flashcards

18 cards on A Level Topic 19, subtopics 19.1 to 19.3. Pick a subtopic or study them all.

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19.1 Principles of genetic technology

Recombinant DNA
DNA made by joining DNA from two or more different sources.
Roles of restriction enzymes and DNA ligase
Restriction endonuclease: cuts DNA at a specific recognition sequence, often leaving sticky ends. DNA ligase: forms phosphodiester bonds to seal the sugar–phosphate backbone.
Why make a gene from mRNA with reverse transcriptase?
mRNA is plentiful in cells making the protein, and the cDNA made has no introns, so bacteria can express it.
Why must a promoter be added with the gene?
It is where RNA polymerase binds. It must be one the host recognises, or the gene is not transcribed.
PCR: the three steps and temperatures
Denaturation, about 95 °C: strands separate. Annealing, about 55–65 °C: primers bind. Extension, about 72 °C: Taq polymerase adds nucleotides. Copies after n cycles = starting copies × 2ⁿ.
Why is Taq polymerase used in PCR?
It comes from Thermus aquaticus, is not denatured at 95 °C and has an optimum near 72 °C, so it survives every cycle.
Gel electrophoresis: why does DNA separate?
DNA is negatively charged (phosphate groups), so it moves towards the anode. The gel acts as a sieve, so shorter fragments move further. A ladder of known lengths gives the scale.
Microarrays: genome analysis vs gene expression
Genome analysis: labelled sample DNA hybridises to complementary probes, showing which sequences are present. Gene expression: mRNA is converted to labelled cDNA; spot brightness shows how strongly each gene is transcribed.

19.2 Genetic technology applied to medicine

Advantages of recombinant human insulin
Identical to human insulin, so fewer allergic or immune responses; a reliable, large supply; no objections to animal sources.
Recombinant factor VIII and ADA
Factor VIII (haemophilia): no risk of infection from donated blood; reliable supply. ADA (a form of SCID): enzyme made in quantity for replacement by injection.
Genetic screening vs gene therapy
Screening tests for alleles (for example BRCA1/BRCA2, Huntington's, cystic fibrosis carriers). Gene therapy adds a normal allele to treat a genetic disease.
Gene therapy for SCID
Remove white blood cells or stem cells, insert the normal ADA allele using a viral vector, and return the cells. Risk: insertion near a cell-division gene has caused leukaemia.
Somatic vs germ-line gene therapy
Somatic: body cells; the change is not inherited. Germ-line: gametes or embryos; the change is inherited, raising consent issues for future generations.
Ethical and social issues of genetic screening
Anxiety about incurable conditions; effects on relatives; discrimination by insurers or employers; embryo selection; cost and fair access.

19.3 Genetically modified organisms in agriculture

GM salmon: gene added and benefit
A growth hormone gene with a promoter active all year, so the fish reach market size sooner on less feed.
Herbicide-resistant soybean: benefit
Fields can be sprayed with herbicide to kill weeds without harming the crop, reducing competition and raising yield.
Bt cotton: gene added and benefit
The Bt toxin gene from Bacillus thuringiensis. Insect larvae that eat the plant are killed, so less insecticide is needed and yield is higher.
Environmental and social concerns about GM crops
Gene flow to wild relatives; herbicide-resistant weeds; insects resistant to Bt toxin; harm to non-target species; seed costs for poorer farmers; control by a few companies; consumer concern.

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